RecyclerView强大的下划线---ItemDecoration_itemdecoration viewtype下划线-优快云博客

本文介绍了如何使用RecyclerView.ItemDecoration来自定义分割线和标签。通过重写getItemOffsets()和onDraw()方法，实现分割线的绘制，同时展示了如何利用onDrawOver()方法在条目上添加推荐、热门等特殊标签。代码示例包括SimpleDividerDecoration和LeftAndRightTagDecoration两个类。

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ItemDecoration类有三个主要的方法,分别如下:

public void onDraw(Canvas c, RecyclerView parent, State state)
public void onDrawOver(Canvas c, RecyclerView parent, State state)
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)

onDraw: 可以实现类似于绘制背景的效果;

onDrawOver: 可以绘制在内容上面 ,将内容覆盖;

getItemOffsets():可绘制在内容周边,类似于padding的效果;

如果需要自定义下划线的话直接继承RecyclerView.ItemDecoration,然后复写getItemOffsets()方法;最后添加到recyclerView.addItem Decoration;

自定义分割线

自定义分割线需要复写getItemOffsets()方法和onDraw()方法, 在getItemOffsets()中得到分割线距离下面条目的距离,在onDraw进行绘制,首先得到需要绘制分割线自身的参数,一共四个坐标;

public class SimpleDividerDecoration extends RecyclerView.ItemDecoration {

    private int dividerHeight;
    private Paint dividerPaint;

    public SimpleDividerDecoration(Context context) {
        dividerPaint = new Paint();
        dividerPaint.setColor(context.getResources().getColor(R.color.colorAccent));
        dividerHeight = context.getResources().getDimensionPixelSize(R.dimen.divider_height);
    }


    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.bottom = dividerHeight;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int childCount = parent.getChildCount();
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();

        for (int i = 0; i < childCount - 1; i++) {
            View view = parent.getChildAt(i);
            float top = view.getBottom();
            float bottom = view.getBottom() + dividerHeight;
            c.drawRect(left, top, right, bottom, dividerPaint);
        }
    }
}

在条目上有时候会加一些特殊的标签,比如推荐.热门等等,那么这些标签就是覆盖在内容上的,就可以通过onDrawOver()方法来实现.

public class LeftAndRightTagDecoration extends RecyclerView.ItemDecoration {
    private int tagWidth;
    private Paint leftPaint;
    private Paint rightPaint;

    public LeftAndRightTagDecoration(Context context) {
        leftPaint = new Paint();
        leftPaint.setColor(context.getResources().getColor(R.color.colorAccent));
        rightPaint = new Paint();
        rightPaint.setColor(context.getResources().getColor(R.color.colorPrimary));
        tagWidth = context.getResources().getDimensionPixelSize(R.dimen.tag_width);
    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            int pos = parent.getChildAdapterPosition(child);
            boolean isLeft = pos % 2 == 0;
            if (isLeft) {
                float left = child.getLeft();
                float right = left + tagWidth;
                float top = child.getTop();
                float bottom = child.getBottom();
                c.drawRect(left, top, right, bottom, leftPaint);
            } else {
                float right = child.getRight();
                float left = right - tagWidth;
                float top = child.getTop();
                float bottom = child.getBottom();
                c.drawRect(left, top, right, bottom, rightPaint);

            }
        }
    }
}

注意: ItemDecoration是可以叠加的

recyclerView.addItemDecoration(new LeftAndRightTagDecoration(this));
recyclerView.addItemDecoration(new SimpleDividerDecoration(this));